Transition-metal Organic Complexes Based Li-ion Flow Batteries

Organic molecules have been demonstrated to be an appealing alternative to Li-ion redox flow batteries.But,comparing with organic molecules,scientists are more interested in organometallics because of their stable structure.As one type of carbonyl group based organic materials,the redox mechanism generally involves the braking and formation of chemical bonds,which would lead to the formation of unstable free radicals.The free radicals may undergo side reactions,so the long-term stability of the cell need extra optimization.However,as one type of organometallics,transition-metal organic complex'redox mechanism simply involve the valence state change of the atom center.There's no intermediate product formed between the oxidized states and reduced state.Furthermore,comparing with organics,the organometallics activation energy required for the orbital electronic structure conversion is very low,and the organometallics redox kinetics is at least two orders greater than that of other organics or other redox couples used in Li-ion redox-flow batteries.Iron-based organic complexes as active material for Li-ion flow batteries A liquid cathode made from transition metal complex,[Fe?bpy?₃]?BF₄?₂ in this study,exhibits high discharge voltage approaching 4 V vs.Li/Li⁺.When coupled with a Li₄Ti₅O₁₂2 anode,the Li-ion full battery exhibits a cell voltage exceeding 2.2 V and decent cycling efficiencies.These results reveal a generic design route towards iron-based complexes as cathode materials with good electrochemical performances.Zn-based eutectic mixture as liquid anode for Li-ion flow batteries Developing greener batteries with new chemistries is a formidable challenge,and will be a major focus for years to come.Redox flow batteries are receiving increasing research interest for grid-scale electrochemical energy storage owing to their unique architecture.However,challenges are still remained by their low energy density as well as corrosive and/or toxic electrolytes.A liquid anode based on aprotic Zn deep-eutectic-solvent,which uses low cost,abundant and environmentally benign materials,exhibits a high solubility of Zn²⁺of 6.25 M and utilizable concentration of Zn²⁺exceeding 1.7 M,resulting in a reversible volumetric energy density of ca.90Ah·L^–1.Combined with high efficiencies and relatively low redox potential of–0.9 V vs.SHE,such a liquid anode provides an alternative way to explore a family of liquid anodes using new chemistries for rechargeable Zn batteries that meet the criteria for grid-scale electrical energy storage.